1. Field of the Invention
This invention relates to optical integrated circuits and, more particularly, to a thermal housing that reduces stresses to its internally housed optical integrated circuit components by minimizing external fiber handling requirements of the housing.
2. Description of the Related Art
Communication systems utilizing optical signals encounter problems that are unique to light wave signal manipulation. These problems generally are not present in communication systems utilizing lower frequency signals, such as those systems which include conductive wires for the transmission of the lower frequency signals. For example, optical switching, multiplexing, and demultiplexing are all operations that present problems. Heretofore, such operations typically have required numerous discrete optical components and, as a result, the systems incorporating these components suffer from increased bulkiness and reduced reliability. As a consequence, much effort has been directed at reducing the number of system components by combining their operations on single, monolithic chip which generally comprises a thin film, compact planar optical circuit.
One example of such a monolithic device is a dense wave division multiplexer (DWDM) of the type shown, for example, in U.S. Pat. No. 5,136,671, issued to Dragone, the disclosure of which is herein incorporated by reference. Such a device is useful where a large number of transmission channels must be crowded into a narrow bandwidth window. Such narrow windows can result, for example, from the use of erbium doped optical amplifiers, which are widely used today, but which can severely limit the usable bandwidth. In order to accommodate many channels in the narrow window, the channels must be closely spaced in wavelength, such as, for example, successive wavelengths differing by 0.8 nm or 1.6 nm.
By use of OASIC (optical application specific integrated circuits) technology, thin film planar optical circuits can be formed to produce such a DWDM as discussed, on a single wafer or chip. Such a chip generally comprises a thin silicon wafer upon which a low refractive index silica glass lower cladding is deposited. A high index core layer is then deposited, patterned, and etched to form the optical waveguides, and then an upper cladding is deposited. Wafers for a variety of functions can be produced using the OASIC technology; however, the remainder of the discussion will be directed to the DWDM in the interest of simplicity and consistency. It should be understood that these other types of integrated circuits are by no means intended to be excluded.
One of the problems arising from the use of some OASIC devices, particularly the arrayed waveguide gratings in a DWDM, is their sensitivity to temperature changes, and to physical stresses which impair their reliability. For example, in the DWDM, because the operating wavelengths of the several individual channels differ by such a small degree, any expansion, contraction or bending due to temperature fluctuations, i.e. temperature fluctuations of less than 1.degree. C., can degrade the optical performance and, in extreme cases, can cause circuit failure.
It has been found that degradation and failure generally can be prevented and reliability of the circuit ensured if the temperature of the device is maintained at a predetermined temperature in a range of 75.degree. C. to 90.degree. C. This maintenance temperature, specific to the individual circuit, must be controlled to within a few degrees Celsius even though the ambient temperature may vary from, for example, 0.degree. C. to 70.degree. C. Thus, some sort of protective housing must be provided for the wafer, i.e. circuit.
Maintaining various types of electronic devices at an even temperature by housing them in sealed containers is well known in the prior art (U.S. Pat. No. 4,968,121 issued to Brusselbach et al., for instance). In any such housing for maintaining a substantially constant temperature in at least a portion thereof, each component within the housing, as well as the housing itself, is subject to deleterious temperature effects during operation. Thus, expansion or contraction of the housing itself due to temperature changes can affect at least some of the components within the housing, to the detriment of the overall operation of the device.
Mechanical stresses also can effect at least some of the components arranged within a housing, with the mechanical stresses typically being associated with the handling of fibers which interconnect the internally housed components with external devices. For example, a typical housing for a DWDM circuit cooperates with a buffered fiber which passes into the housing for carrying input optical signals to the DWDM. The output signals of the DWDM circuit exit the housing, such as through a ribbon fiber, with each fiber of the ribbon fiber including a jack plug at its terminated end that is arranged external to the housing. So configured, improper handling of the buffered fiber or of the ribbon fiber can transmit mechanical stresses to the internally housed components to which the fibers are connected. Additionally, improper bending of the fibers caused by external handling or improper interior fiber storage, among others, can result in increased signal loss and/or fiber stress and also can result in fiber to waveguide joint instability, and possibly failure.
Therefore, there is a need to provide thermal housings that address these and other shortcomings of the prior art.